(1) Field of the Invention
This invention relates to an ignition timing controller e.g. gasoline engine (sparking engine), which is equipped with a variable swirl forming means for changing over the swirling state of an air stream, which is flowing into an intake port, in accordance with the operation zone.
(2) Description of the Prior Art
An ignition timing controller for a gasoline engine (sparking engine) has heretofore been composed a crank angle sensor for detecting the crank angle of the engine, a standard ignition timing determining means for receiving a detection signal from the crank angle sensor and determining the standard ignition timing of the engine (this standard ignition timing is set at 0.degree. when a specific cylinder is in a specific phase) and at least one spark plug provided with each cylinder of the engine as an ignition means for inducing an ignition in the combustion chamber of the cylinder responsive to a standard ignition timing signal from the standard ignition timing determining means as well as an ignition timing correction means for either retarding or advancing the standard ignition timing in accordance with the coolant temperature, the intake air temperature and the degree of knocking.
On the other hand, a variety of variable swirl forming devices have also been proposed to form swirls selectively in an air stream, which is flowing into a combustion chamber from an intake port, depending on the state of an engine, for example, the state of its rotation.
It has also been proposed that the above-mentioned ignition timing correction means has an ignition advancing map for a lean burn feedback control (hereinafter called "L-FB ignition advancing map") and another ignition advancing map for a control other than the lean burn feedback control (hereinafter called "non-L-FB ignition advancing map") in order to control the air/fuel ratio depending whether the variable swirl forming device is actuated or not.
With such an ignition timing correction means, it is practised to set the L-FB ignition advancing map at a required advancing value corresponding to an operated state of the variable swirl forming device (occurrence of swirling) and the non-L-FB ignition advancing map at another required advancing value corresponding to the non-operated state of the variable swirl forming device (straight air stream without occurrence of swirling).
Since the degree of an advance of the ignition timing is not corrected in accordance with the actual state of operation or non-operation of the variable swirl forming device in such a conventional ignition timing controller for an engine, an ignition advancing map selected in accordance with the state of the engine may not conform with the state of swirling corresponding to the thus-selected ignition advancing map during malfunction of the variable swirl forming device or in a transition period such as a delay in response of the variable swirl forming device.
In other words, problems such as surging (irregular combustion) and a reduction to the power output of the engine arise due to a reduction in the combustion velocity if an intake air flow is in a straight state at the time of selection of an L-FB ignition advancing map. If the intake air flow is in a swirling state at the time of selection of a non-L-FB swirling state, there is a possible inconvenience of knocking.